The human knee joint is supported by four major ligaments, including:
1. the fibular collateral ligament, arranged on the outer (lateral) side of the knee. This ligament is attached to the outer prominence of the thigh bone (the lateral femoral epicondyl) and stretches to the lateral side of the shin bone (tibia);
2. the medial collateral ligament, arranged on the inner (medial) side of the knee. This ligament is attached above to the inner prominence of the thigh bone (the medial femoral epicondyl) and below to the medial aspect of the tibia;
the central (cruciate) ligaments which cross in the center of the joint, including
3. the anterior cruciate ligament attached from the femur to the front of the tibia; and
4. the posterior cruciate ligament attached from the femur to the rear of the tibia.
The knee ligaments prevent abnormal motion of the knee and permit normal motion of the knee. All ligaments are taut when the knee is straight (extension) and are lax when the knee is bent (flexion). The anterior cruciate ligament prevents excessive forward displacement of the tibia in relation to the femur.
Excessive stress on the outside or inside of the knee joint will tear the ligaments. Athletic injuries, some of the most common knee injuries, occur when the foot is fixed on the ground while the thigh rotates inward and the leg outward, creating stress on the ligaments on the inner side of the knee. The anterior cruciate ligament may also be injured when the tibia is pushed too far forward on the thigh bone.
In most mild injuries to the knee ligaments, complete mobility may be restored if the joint is immobilized to allow the ligament time to heal. However, more severe injuries may leave permanent stiffness or lack of complete mobility, but the chance for recovery is increased if the ligament can be immobilized for a period of time.
It has been well known to use a knee brace to support an injured knee joint. Previous knee braces have been mainly concerned with providing support and preventing abnormal movement of the knee, such as over-extension, over-flexion or rotation of the joint. To accomplish this effect, previous devices have been constructed to include means on both the lateral and the medial sides of the leg to attach the brace to the leg and a hinge located at the center of the axis of rotation of the knee joint.
A known type of hinge used in prior knee braces consists of a bicentric geared hinge where there are often stops associated with the hinge gears for limiting the extent of flexion and extension.
The problems associated with these types of knee braces include the fact that they do not provide the forces necessary to act as the anterior cruciate ligament in order to prevent the tibia from moving forward of the femur. Anti-drawering is the term given to the effect of preventing the tibia from moving forward of the femur. The treating physician will often want to control the amount of anti-drawering effect of a knee brace depending on the severity of the injury and the individual characteristics of the patient's bone structure. Most of the previous devices include straps that encircle the leg to attach the brace to the leg. Some braces include rigid shells that are held onto the leg by straps. Neither of these arrangements provide the forces on the various parts of the leg necessary to keep the tibia in proper alignment.
The device disclosed in U.S. Pat. No. 4,697,583, to Mason et al. ("Mason"), purportedly provides the forces necessary to act as a substitute for the anterior cruciate ligament. The device disclosed in Mason includes strategically placed rigid and adjustable straps attached to rigid bars on either side of the leg both above and below the knee that create a force couple on the knee joint which forces the tibia backward into alignment in relation to the femur. The bars are designed to conform to the general shape of the bones, including a curved portion which is immediately adjacent to the knee. The Mason patent also discloses a bicentric hinge to provide for movement and the hinge includes stop means to control the extent of knee extension and flexion. The device disclosed in Mason does not, however, allow for any adjustment of the anti-drawering effect and therefore, no adjustment of the relative position of the tibia and the femur. Because of its arrangement, with the attachment bars having a set curvature to account for the natural position of the bones, the device disclosed in Mason cannot be adjusted to fit the particular anti-drawering needs of an individual patient, especially with respect to the patient's changing anti-drawering needs as the postsurgical healing process progresses.
The straps of Mason which attach the brace to the leg only encompass a portion of the leg and therefore, the rigid straps must be individually formed to fit an individual's particular leg size or the straps must be made in general leg sizes which may cause discomfort to the patient.